The invention relates generally to systems and methods for assessing wear or damage to turbine parts and more specifically, to wear in a shroud of the turbine.
There are several techniques that are currently used for inspection of turbine parts. A commonly used technique includes schedule-based shutting down of a turbine and physically examining parts at predetermined intervals. However, the process is inefficient, time consuming, and costly due to turbine shut down and maintenance. Further, several on-line methods have been developed for detecting wear-out of turbine parts such as, but not limited to, shrouds.
For example, Blatchley and coworkers (C. C. Blatchley and R. J. Bricault Jr., in Tribological Mechanisms & Wear Problems in Materials, ASM International, Metals Park, Ohio, 1987, pp. 95-100 and C. C. Blatchley and P. G. Loges, in Advances in Steam Turbine Technology for Power Generation, ASME, New York, N.Y., 1990, Vol. 10, pp. 9-13) developed a “surface layer activation” technique to monitor wear and corrosion in steam turbines by detecting gamma-ray signals from radionuclides imbedded in trace amounts in surfaces of wearing parts. The nuclides served as surface markers, and were produced by controlled exposure to particles from Van de Graaff or cyclotron accelerators.
However, the above techniques can only be applied to steam turbines, which are closed systems, so that radioactive materials in the water stream will not be released to the environment. The technique cannot be applied to gas turbines because the exhaust is released into the air, and radioactive elements will be detrimental to the environment. Also, a gas sampling and analysis system would be needed in the area of the exhaust stream if one decided to use this technique on gas turbine engines. This technique further finds challenges in aircraft engine systems where the sampling and analysis system needs to occur online or during flight, thus increasing the complexity.
There are other existing coating life estimation methods that are typically based on average effects of stress and temperature profiles of the parts. Such methods are unable to focus on individual parts since they do not take into account conditions that the parts installed in a particular turbine actually encounter, such as, but not limited to, foreign object damage, variation of operating conditions from site to site, and occasional overfiring of the turbine. All of the conditions can drastically influence the true remaining life of the individual parts. Blade rubs also contribute to conditions where a small portion of the shroud may experience more localized damage than the rest of the shroud.
Thus, there exists a need for an on-line assessment of wear of gas turbine parts that addresses one or more aforementioned issues. In applications that utilize a clearance control system, since clearance measurements typically measure the distance between the installed sensor and the blades and assesses the blade to shroud clearance based on the expected shroud thickness, accurate assessment of the extent of shroud wear is necessary to maintain the clearance measurement accuracy of the system.